TABLE OF CONTENTS Polyesters are important thermoplastic resins, which can be obtained by the condensation reaction of glycols and acids or anhydrides {798163}. For example, the condensation polymerisation of ethylene glycol or butylene glycol and terephthalic acid produces the well-known polyesters, poly(ethylene terephthalate) (PET) or poly(butylene terephthalate) (PBT), respectively. The mechanism of thermal degradation of polyesters has been studied for many years {817822} {776328} {756176} {670828} with the help of model compounds. However, there is still some current controversy on the crucial point whether the primary thermal decomposition reactions that occur in polyesters involve radical or ionic processes {777330} {490068}.
Studies on the thermal stability of the di- n-alkyl esters of poly(itaconic acid) show that depolymerisation is the main mode of degradation mostly initiated at the chain ends due to the presence of chain-end unsaturations [a.147, a.148]. The extent of this mode of initiation is much greater than for the corresponding esters of poly(methacrylic acid). This has been ascribed to the introduction of chain-end unsaturations during chain transfer to monomer in radical polymerisation [a.148]. Thermogravimetry studies performed on poly(di- n-propyl itaconate) (PDnPI), poly(diisopropyl itaconate) (PDiPI), poly(di- n-butyl itaconate) (PDnBI), poly(diisobutyl itaconate) (PDiBI) and poly(di- sec-butyl itaconate) (PDsBI) show that PDiPI and PDsBI thermally degrade in a similar manner, with deesterification, together with depolymerisation, being a significant mechanism [a.148]. PDnPI and PDnBI also degrade in a similar manner by depolymerisation, with chain-end initiation being more important than random main-chain scission initiation. The results for PDiBI indicate more...
